The present invention relates to transmitting and receiving systems.
Recently, a spectrum diffusion system in which the transmitting spectrum is diffused and a wide frequency band is commonly used is attracting attention.
In such a spectrum diffusion system, a kind of code (this code is referred to as a pseudo noise code) is given into the spectrum and modulation is performed and only the signal having the code is demodulated independently of the other signals. By changing the code, a large number of communication channels can be set. On the other hand, as compared with conventional other communication systems, the spread spectrum system has advantages such that it is strong against noise or interference and a message screening from eavesdroppers or low density power spectrum for signal hidding is obtained and the like; therefore, various uses of this technique are being examined.
A spectrum direct spread spectrum system is known as one of the foregoing systems. According to the system, the receiver side needs to obtain synchronization with the pseudo noise code to perform modulation on the transmitter side. In general, a process such as delay lock tracking, taw dither tracking, or the like is performed. (For example, refer to "Spread Spectrum System", R. C. Dixon, John Wiley & Sons Inc., 1976.)
Therefore, in the receiver side, the construction becomes complicated and it takes time to preliminarily obtain synchronization.